Flexible copolymers of p-(hydroxyalkoxy) benzoic acid or its methyl ester are disclosed in U.S. Ser. No. 253,418. As set forth in the "Background of the Invention" in that application, p-(hydroxyalkoxy) benzoic acids had been used in fibers and films which exhibited good strength, but their copolymerization with flexible chain components to produce flexible copolyesters had not been suggested. The present invention comprises a novel diester and method of making the same which diester may be used to produce the p-(hydroxyalkoxy) benzoic acids or their methyl esters of the prior application or to produce the flexible copolyesters of the prior application directly from the diester, without the intermediate step of producing the p-(hydroxyalkoxy) benzoic acid or its methyl ester. The use of the diester produces greater yields and enhanced purity of the p-(hydroxyalkoxy) benzoic acid or its methyl ester.